Synchrotron radiation induced surface photovoltage at metal/GaAs interfaces

We use the Kelvin method to study the synchrotron radiation induced surface photovoltage (SPV) on GaAs(110) as a function of metal coverage and temperature. We find that varying the temperature alone does not induced significant change in band bending in the semiconductor, but that the combination of low temperature and synchrotron light illumination on lightly doped n-GaAs induces a large and quasi-permanent SPV. On lightly doped n-GaAs, the low-temperature SPV (0.55 eV) is equal to the quasi-totality of the band bending at submonolayer coverage and discharges with a time constant of the order of hours. Above a monolayer, the rate of discharging increases dramatically, emphasizing the role of charge leakage through the overlayer. The room temperature SPV is considerably smaller (0.2 eV). Finally, no significant SPV is detected on highly doped GaAs. The impact of this synchrotron radiation induced SPV on the photoemission study of metal/semiconductor interfaces is discussed in detail.